Although it is commonly known that “smoking is harmful to your health”, the number of smokers worldwide is up to 1 billion, and the number is increasing every year. According to the statistical data from the World Health Organization, about 4.9 million people die of smoking diseases each year. Although smoking may cause serious respiratory diseases and cancer, it remains extremely difficult for smokers to quit smoking completely.
The active ingredient in a cigarette is nicotine. During smoking, nicotine, along with tar aerosol droplets, enter the smoker's alveolus and are rapidly absorbed. The nicotine then affects the receptors of the smoker's central nervous system.
Nicotine is a kind of alkaloid with low molecular weight. A small dose of nicotine is essentially harmless to human body and its half-life in blood is quite short. The major harmful substance in tobacco is tar. Tar in tobacco is composed of thousands of ingredients. Several of these are cancerogenic.
Some cigarette substitutes that contain only nicotine without tar have been proposed. Many of them, such as “nicotine patch”, “nicotine mouthwash”, “nicotine chewing gum”, “nicotine drink” etc., are made of pure nicotine. Although these cigarette substitutes are free from tar, their major disadvantage is that an effective peak concentration can not be reached in the blood of a smoker due to slow absorption of nicotine. In addition, these cigarette substitutes can not satisfy habitual smoking actions of a smoker, for example, inhaling action, and thus are not likely to be widely accepted as effective substitutes for smoking.